The present invention relates generally to inflators or gas generators for air bags and more particularly, to a hybrid inflator.
U.S. Pat. No. 3,895,821 is illustrative of a hybrid inflator. As can be seen from this reference, the hybrid inflator includes a pressure vessel filled with a predetermined quantity of pressurized inert gas. One side of the pressure vessel is closed by a rupturable disk. Upon ignition of propellant, the gas pressure within the pressure vessel increases to a level sufficient to rupture the disk. Thereafter, heated gas exits one or more exit ports to inflate a nearby positioned air bag. U.S. Pat. No. 3,758,131 is illustrative of a second, though related type, of hybrid inflator in which two (2) propellant charges are placed within the pressure vessel. Depending upon the intensity of a crash, one or both propellant charges are ignited. The dual charges provide a greater degree of control of the rate at which gasses flow from the inflator and into the air bag. Each of the above patents includes an initiator, or squib which when activated by a control signal, starts the burning of the closely positioned propellant.
One deficiency of many hybrid inflators is that it takes a relatively long period of time for the pressure inside the pressure vessel to build up a level sufficient to burst the rupture disk leading to an exit port. In prior art inflators in which the generant is located in a propellant chamber that is at atmospheric pressure, the time it takes for the inflation gas to exit the inflator consists of the time needed to increase the pressure about the generant, that is within the propellant chamber, to a level in excess of the back pressure of the inflation gas (which typically acts on a seal disk, which typically isolates the propellant chamber from the pressure in the pressure vessel) and then the time needed for the gas to exit the propellant chamber and enter the pressure vessel. During this time the mass flow of the hot propellant gases must continue until the pressure in the pressure vessel reaches a level sufficient to break the burst or rupture disk allowing inflation gas to exit the inflator.
It is an object of the present invention to provide an improved hybrid inflator. Another object of the present invention is to provide a hybrid inflator in which the time from initiation to the bursting of the rupture disk is shortened while still retaining a controlled gas generation rate of the propellant.
Accordingly, the invention comprises: a hybrid inflator comprising: a pressure vessel including a central member closed at its ends by a first and a second closure member. One of the closure members includes a means for introducing pressurized inflation gas into the pressure vessel and the other of the closure members includes a breakable (rupture or burst) disk in communication with at least one exit port. A pyrotechnic container is provided, within the pressure vessel, and is secured at one end to one of the closure members and includes a plurality of vent openings about its wall. A first quantity or main charge of pyrotechnic material, is located within the pyrotechnic container for providing a first controlled gas generation rate. This main charge also provides the primary means of heating the inflation gas in the pressure vessel. A second quantity or secondary charge of pyrotechnic material is located at least partially within the main charge and is characterized by a faster gas generation rate than the gas generation rate of the main charge. This secondary charge produces products of combustion that ignite the first quantity or main charge of material. A portion of these products of combustion initially rapidly heat the inflation gas opening the burst disk. Means are provided for igniting the second quantity of pyrotechnic material.
Many other objects and purposes of the invention will be clear from the following detail description of the drawings.